Electrical circuit breaker



Feb. 12, 1952 WOOD 2,585,068

ELECTRICAL CIRCUIT BREAKER Filed Feb. 28, 1947 TEMPERATURE Patented Feb. 12, 1952 U N I T E D STAT ES PATENT OFF ICE 2,585,068 ELECTRICALCIRCUIT BREAKER Morris B. Wood, Newbury; Mass. ApplicationFebruax-y28, 1947, Serial No. 731,461

7 Claims... (01. aim-113) The present invention-relates to improvements: in electrical overload: circuit breakers of the type employing a bimetallic strip heated ,bycurrent flow as the sole operating member.

A simple bimetallic strip of the usual constructiontfiexes upon .heatingaand requires a rapid. change in temperature .to :insure quickzpositive.

movement. To 'insure.'.positive movement. with arranged with an oppositely acting portion in'the' small. changesofr temperature and. to avoidirregular action, itis .commonxto connect a bimetallic strip with a snapmechanism, but such mechanism introduces difiicultyin. calibration, irregu,.- larity of friction-and uncertain lost motion. For.

a circuit controller oflow current. carrying. .ca:

pacity an operating memberof bimetal without. snapmechanism has been. f ound. practical. where 1 it is desired to operate thestrip. upon changes of, ambient temperature only; Tov reduce arcing. at.

the contactsof such controller the. strip is ar..-. ranged in some instances with a short auxiliary portion acting in a direction opposed to the main;

operating portion of the strip,=the. opposed porsuch breaker reaches the annealing or melting tion being heated by current flowingthrough the contacts. The opposed portion of the stripwhen. heated tends tohold the contacts closeduntil thev force 01- the main" operating portion overcomes that of the opposecl portion and the-contacts start to separate.

The flow of current is their 1..

reduced and theopposed strip portion is allowed...

to cool. Cooling the opposed portion opens the contacts still further and reducesarcing or chattering.

An arrangement era bimetallic strip type circuit controller with an oppositely acting stripportion, being ordinarily subject to almost imperceptible heating from current 'flowalone, does not present serious problems in heat'dissipation.

In fact, it is desirable to concentrate the heating from current flow on theopposed portion of such strip. To do this the movable'contact is mounted.

directly on the opposed portion of the strip toenable theheat from'the contact to be conducted to the opposed portion: The opposed strip per-- tion is in turn supported by the main operating portion of the strip and the main portion is anchored to a terminal post.

The requirements of a reliable overload circuit breaker are moredifiicult tomeetthan those of a low current controller, a circuitbreaker being subject to intense" heating well above ambient temperatures. If an attempt is made to employ a circuit controller havinga bimetal'opera tor of prior construction and arrangement; uniform circuit openings with varying intensitiesof overloads do not occur. If'a bimetallic strip is usual manner, the opposed portion will. be sub; jected to injurious or disruptive temperatures.

before circuit opening can take place on over.-

loads of great magnitude. For instance, in an. overload breaker intended to protect a six to twelve volt circuit, opening must occur reliably within a range of from 15 to. 600 amperescurrent flow withoutinjury tothe breaker. The intensity vof heating produced. inthebimetallic strip. of

point of the strip and contactswithina small fraction of a second, particularly ifltheheat is concentrated locally so that there is .anii'regular ;.temperature gradient. along the length ofthe.

"strip, rising sharply. at the contact carryingend of the strip.

The objects of the present inventionv are. to.

provide. an. overload circuit breaker, operated solely from a bimetallic strip heatednormally above ambient, temperatures by. current flowing in,the .circuitto beprotected, which breakeris of extremely simple 5 and inexpensive I construe tion and yet capable of..withstandingrthe;heat-- ing effects; of. repeated. short. circuitsundereall operatingnconditions withoutiailure. or; loss; ofs. sensitivity to overloads of smallimagnituder. A.'..

further object. of the-inventionis-toiprovide such tion of the stripbeing arrangedin opposed=-rela-- tion to the main operating portionof the strip in such manner thata sharply rising temperature gradient along thestrip is=avoided;'whilethepertions of the strip are 'heated'difierently andbot'h substantially above the ambient temperature-by;

normal currents in thecircuit- 'With the contacts; In this-way-the'iull length of the main operating" portion of the strip is quickly renderedresponsive at all times for circuit" opening action-and the circuit is always-opened'b'efore disruptiveheating" occurs: Also, local concentration of" heat in the-" strip is prevented. An'importantadvantage of"- the invention which contributes to'its effectiveness is obtained in the proportioning of the bi metallic strip along itslength to produce'a tern-" perature gradient which approaches a uniform" vvalue or which may even droop-toa slightly lower- 3 temperature towards the contact carrying end of the strip.

This feature of the invention is embodied in a bimetallic strip circuit breaker having a main strip portion of lower electrical resistance per unit or" length but of predominating deflection and an oppositely acting auxiliary portion of higher resistance per unit of length but of shorter denection connected thereto, the main portion being bent into a U shape with one arm carrying the movable contact at its inner side. Preferably, the opposed portion or" the strip is relatively straight and supports one arm of the main operating portion in close parallel relation and is in turn mounted upon a terminal post which produces rapid cooling action by conduction of heat from the reverse portion.

These and other features of the invention include a novel and improved controller containing the circuit breaker embodying the principle feature of the invention, as well as certain novel constructions, combinations and arrangements of parts hereinafter described and claimed, the advantages of which will be apparent from the following description taken in connection with the accompanying drawings, in which:

rig. l is a view in sectional plan view of a controller embodying the features of the present invention as seen along the line l-l of Fig. 2.

Fig. 2 is a side sectional view of the controller illustrated in Fig. 1;

Fig. 3 is a sectional view taken along the line 3-3 of Figure 2;

Fig. 4 is a side detail view of the breaker illustrateu in Fig. 3 with cover removed showing the position of the parts in an intermediate position of increased pressure on the contacts during normal current flow;

Fig. 5 is a similar view of the breaker taken at the moment of opening a circuit;

Fig. 6 is a diagrammatic view illustrating the manner in which the opening action of the breaker accelerates with greater magnitudes of overload current flow; and

Fig. 7 is a diagrammatic view illustrating the temperature gradients along the strip under different conditions.

The circuit breaker illustrated in the drawings is constructed with a single unitary non-snap bimetallic operator to provide overload protection ror low voltage circuits such as are employed in automotive or similar usage. Upon the occurrence of an overload, the circuit is held closed for an instant of time, the length of which is shorter the greater the overload, and then the circuit is opened quickly. The breaker has the usual terminal posts [0 and 12 fast in an insulating base Hi. The bimetallic operator is in the form of an integral strip formed with layers of metal having different coefiicients of expansion at its opposite sides and mounted at one end on the post l2. At the other end the strip is provided with a movable contact l6. The movable contact is secured by welding to the high expansion side of the strip so that the current passing through the contacts affects the entire length of the strip. Cooperating with the movable contact is a contact l8 fixed by welding to the terminal post 10. The strip is made with such a cross-sectional area and with such initial shape and tension that it will be heated throughout its length by normal current flow within its intended rating substantially above the ambient temperature before the contacts are opened.

In the construction of a bimetallic strip operated circuit controller intended for response to ambient temperature changes having in its bimetallic strip a main operating and an opposed portion for avoiding sluggishness and excessive arcing at the contacts, the opposed portion is secured in heat and electrical conducting relation to the main operating portion with sides of similar coeflicient of expansion together and is formed with a reduced cross-section to provide a relatively high resistance, the main operating portion acting to close the contacts against the contact opening action of the auxiliary portion. The current in the circuit controlled by such device is small and in order to obtain as much benefit as ossible from the opposed portion of the strip the movable contact is mounted upon it. In this way the opposed portion of the strip is heated more when any arcing occurs at the contacts and is flexed thereby to press the contacts together until positive opening occurs. Upon cessation of current flow a maximum flexure of the strip toward circuit opening position takes place.

If an attempt is made to employ a circuit breaker construction similar to that used for ambient temperature control reliable protection cannot be ensured. With a high resistance highly heated portion at the free contact carrying end of the bimetallic strip there will be a local concentration of heat at the contact carrying end, causing a steep temperature rise at the movable contact. With a dead short circuit the temperature at the movable contact will quickly reach a destructive or injurious value. Furthermore, a circuit protected by a breaker constructed according to prior practices is not maintained open indefinitely but only long enough to cool the main portion of the bimetallic operating strip. Thereafter the circuit is reclosed. A circuit breaker in which the bimetallic operator is subject to a local concentration of high temperature will not remain in open position long enough to cool the high temperature portion but will reclose as soon as the main operating portion is cooled. Continued opening and closing will therefore quickly build up the temperature of the locally heated portion above a destructive value. Thus, the operation of a circuit breaker having a bimetallic operator according to prior ambient temperature controller designs is lnefiective for the present purposes.

To ensure uniformly reliable protection in a self-reclosing overload circuit breaker having an auxiliary circuit closing strip portion secured in direct electrical and heat conducting relation to the main portion, and to avoid destructive heating in its bimetallic strip and contacts, according to the present invention, the strip is arranged to be heated substantially above the ambient temperature throughout the main operating portion of its length by normal current flow and the main and auxiliary portions are reversed from their usual positions. The auxiliary portion of the illustrated strip is indicated at 20 and acts to increase the pressure on and maintain the contacts closed briefly upon heating above the ambient temperature. The auxiliary portion is secured in heat and electrical conducting relation to the terminal post l2 and is narrower than the main portion (see Fig. l) and is of relatively high resistance per unit of its length as compared with the main operating portion of the strip and accordingly the auxiliary portion has a tendency to heat more rapidly than the main operating portion of the strip, indicated at 22. For this reason also the reverse portion is heated well above the ambient temperature. However,

the" auxiliary strip portion is 1 shorter thaIf -themain operating portion 22 and consequently con circuit opening action when heated above 'theopening temperature. Thus, both portions along thee'ntire length of' the strip being of difierent cross-sectional area are kept' heated substantially above ambient temperatures 50 that there is an ac'tive flow of heat away fromthe strip'at alltlmeswithnormal currents within-the rating 1 of th't-i breaker; In this way the strip is keptin a qulckly 'responslve condition the instant the tei'iiperature- 'of-themain operating portion 22' rises" abo've the pr-edetermined operating point.

To-further ensureagainst local heating of the strip the auxiliary portion 20, being mounted uponthe-terminal post i2 is cooled directly by rapid conduction while the main operating por tioii 22- is cooledonly by heat dissipation to the air or'through the contacts when the breaker is closed. The conduction of heat from the strip throughthe contacts is relatively small in comparison to that through the terminal post by reason of its direct heat conducting mounting on theterminal post. While the breaker is in open circuit -position the temperature of the main operating portion of the-strip therefore, quickly reachesa uniform value and even when the circult is closed thetemperature of the contact carryi'ngen'd of the portion 22 is reduced only slightly by conduction through the contacts.

Referring to Fig. 7, the temperature gradient along the length of the bimetallic strip with normal" currents for the circuit breaker is illustrated by the curve 24, running from the ordinate at the terminal post [2 to its upper end at the contact [6. The-broken line 23 represents th'e'amb'ie'nt" temperature of the air and the dot dash line 26 the temperature of the bimetallic. strip atwhich circuit opening occurs. From this curve it'is apparent that the main operating portion 22 of the stripis heated with a temperature" gradientwhich approaches a constant value.-- As the temperature-of the strip-increases above the ambient value With increased current flow-L the temperature gradient approaches "a parallel relationto the opening temperature line 26;": As soon-as-the line 25' is crossed, as in curve 28; practically the' full length of the main operating' po'rtion 220i the strip is acting to openthe contacts-'- In this way all tendency to'slugg-ish action from improper heat distribtution in the strip is avoided. Even when the contacts close again the'heat is conducted from the outer end of the strip-at a relatively slow rate so that there is only a slight droop to a lower temperature at the end of the gradient.

By keeping the high resistance auxiliaryportion of the bimetallic strip cooler throughconduction; than the lower resistance main operating portion of the-"strip, the full benefit of" the are reducing action of the auxiliary portion is obtained and localheating of the strip above the temperature of the main operating portion of the strip-is definitely prevented. Since the main operating portion of the strip is heated with a temperature gradient approaching a parallel relation-to the-opening temperature line throughout the entire length of the main operating portion, the-maximum temperature at any point on the main operating portion can never exceed greatly to cool.

in which a highresistance portion is not keptcooler-thanthe lower resistance portion and in which points of extremely high. temperature are allowed to build up to a destructive value.

With reliable operation ensured by the manner of construction above described, the calibration I and'performanceof the improved circuit breaker,

canbe'determined more exactly and with .cer

tainty; Referring to Fig. 6, it will be apparent".

that'for'a breaker designed for opening on currents above 2oamperes at-6 volts, the time dur ingwhich the circuit remains closed after an overload current begins tofiow is represented for an overload currents up to 300 by the curve After having opened the circuit for a given overload it will remain open at the time indicated'by a point onthe curve 32;

30 marked, on time."

marked oil? time, directly above that selected on the on time curve.

an overload current is permitted to flow varies from less than a second to more than three seconds. The times at which the circuit remains open varies from three seconds to more than' twenty, the ordinates being measured loga-' rithmicaliy. The ofi time periods increase in length at a rapidly progressing rate with higher overload magnitudes sothat adequate cooling of the heated parts is ensured during the oil times. It is for this reason that the breaker of the present invention is able to continue in operation successfully where prior breakers of the bimetallic type have failed.

It will be noted in connection with the on time curve 30 that there is much less drop inthis characteristic than there is in rise in the off time curve 32, hearing in mind that both curves are plotted on a logarithmic scale "which has largeunitsat itslower end and units of progressively decreasing height at its upper end,

so that for the same vertical distance the curve 3% indicates a smaller time interval than the By proportioning the bimetallic strip curve.32. 2c, 22 in this Way the on time interval with overloads caused by a few frayed and grounded" iree action of this type because of its uniformity in opening a short circuit before destructive temperatures are reached Within the breaker itself. This advantage is not obtainable with the use'of prior circuit protecting devices of the fusible link or snap mechanism type since thevention illustrated in Figs. 1 to 5 is a circuit breaker of extremely compact construction for use where it is desirable to maintain a minimum spacing between the terminal posts H] and I2.

Theauxiliary portion 20 of the bimetallic strip is welded directly to the high resistance mainpor tion 22-with sides of dissimilar coefiicien't or" errpansion together atthe welding point and com'' prises a relatively straight strip piece. The mainfl operating'po'rtion 22'0fthe-Strip is bent-into 'a- U shape with one arm of the U longer'than'the As indicated by these curves, the time measured vertically at Which- The 7 other. The longer arm of the U carries the movable contact l6 at its inner side so that when the end of the shorter arm is integrally connected to the auxiliary portion 20 or the strip it will be close and approximately parallel to it. Care must be taken in securing the two portions of the strip together not to permit them to touch except at the point of securement. Otherwise a substantial length of the operating portion will be electrically short-circuited. Although the two strip portions preferably are secured together by welding, riveting also produces effective results.

With a straight auxiliary strip portion 20 and a U-shaped main operating portion 22 connected together in electrical and heat conducting relation in the manner indicated, the movement of the two portions under normal and overload currents is illustrated in Figs. 4 and 5. When the strip is cold and at ambient temperature, a position is assumed similar to that of Fig. 3. When a normal current flows through the breaker below an overload value, the auxiliary strip portion 20 bends downwardly, pressing the contacts more firmly together as in Fig. 4. Upon heating by an overload current flow, the movements of the main operating portion of the strip predominate, having been heated above an opening temperature. Eventually, a slight separation of the contacts occurs, producing a sudden concentration of heat in the contact end of the main strip portion 22. A quick movement of contact separation is then produced, interruption of current ilow causing a continued separating movement of the contacts toward fully open position as the auxiliary portion cools (Fig.

It may be desirable to provide a well 33 in the base H to prevent engagement of the strip with the base. The arrangement of the U-shaped main and straight auxiliary portions of the strip reduces to a minimum the tendency of the movable contact to slide on the fixed contact. In this way a firm contact engagement is ensured at all times with the movement of the movable contact restricted when opening the circuit to that perpendicular to the engaging surface of the fixed contact. I

In applying a self reclosing circuit breaker of the type described above to a unitary automotive lighting circuit controller as an example, the breaker is covered with a drawn housing 46 locked to the rabbeted edge of the base I4. To connect the breaker with a two-way manually operated lighting switch, a thin fiat flexible conductor 48 is fastened to the terminal post Hi. The conductor 48 extends at right angles to the length of the breaker base and is yieldingly clamped between a movable contact 55 in the switch and an insulating contact actuating member 52 pressed against the fiat conductor which in turn presses the movable contact 50 against a fixed contact 54. The flat conductor 48 thus is interposed between two parts pressed yieldingly together and may be inserted or removed in assembling 0r dissembling the controller without special manipulations.

For ensuring proper operation of the controller, the movable contact 56 is formed in the shape of a cross with two bent up ears 56 engaging diametrically opposed recesses in the insulating disk 52. To operate the controller, the disk is notched outside its points of engagement with the movable contact to receive the extremities of a manually operated yoke 58 having fixed to its central portion an operating spindle 60 rotatable in an outer housing 62. At its end outside the housing, the

spindle is slotted for connecting a knob or similar manual operator. Between the yoke and the disk 52 is compressed a coil spring 64 for applying the yielding force to clamp the conductor 48 and press the movable contact against the fixed contacts. To provide a firm connection the movable contact is dented upwardly or the disk dented downwardly at their centers of rotary movement so that the points of engagement between the movable contact and the conductor 48 will not change while operating the switch.

By arranging the parts in this way the controller is readily assembled and dissembled merely by bringing the parts into proper operating relationship. The entire controller comprising the manual switch and the overload circuit breaker thus forms a complete assemblage. For maintaining the parts together in this way they are mounted upon a single insulating base 6S perforated and otherwise shaped to accommodate them.

Under extreme conditions not intended to be coped with by the illustrated circuit breaker, the construction hereinbefore described has the inherent advantage that the high resistance portion of the bimetallic strip will melt and act as a fuse before the low resistance portion is disrupted. The fuse action of the high resistance portion is desirable whether the contacts become welded together before fusing occurs or not. If the contacts are welded together when the high resistance portion 20 is fused the lower resistance portion 22 will tend to move away from the terminal post i2 as long as any current continues to flow, thus aiding in breaking the circuit. If the contacts are not welded together the portion 22 will drop off if the portion 20 is fused so that the circuit will be broken positively under any extreme overload.

The nature and scope of the invention having thu been indicated and an embodiment having been specifically described, what is claimed is:

1. An overload circuit breaker having fixed and movable contacts, and a pair of heat conducting terminal posts, one of which supports the fixed contact, in combination with an integral bimetallic strip having one end mounted on the other terminal post to open the contacts upon heating above a predetermined temperature by current flowing through the contacts, and an auxiliary movable contact actuating portion of the strip being disposed in oppositely acting relation to the remainder of the strip to cause an increase in the pressure on the contacts below the opening temperature, the remainder of the strip comprising a main contact opening portion bent into U shape with one arm carrying the movable contact and of lower electrical resistance per unit of length than the auxiliary portion of the strip.

2. An overload circuit breaker having fixed and movable contacts, and a pair of heat conducting terminal posts, one of which supports the fixed contact, in combination with an integral bimetallic strip, having one end mounted on the other terminal post to actuate the movable contact away from the fixed contact upon heating above a predetermined temperature by current flowing through the contacts and main and auxiliary portions, the auxiliary portion of the strip being disposed in oppositely acting relation to the main operating portion to cause an increase in pressure on the contacts when heated below the opening temperature, the main operating portion of the strip being bent into U shape with one arm 76 carrying the movable contact and the auxiliary portion of the strip being relatively straight and supporting the main operating portion with one arm of the U in close parallel relation.

3. An overload circuit breaker having fixed and movable contacts, and a pair of heat conducting terminal posts, one of which supports the fixed contact, in combination with an integral bimetallic strip having main operating and auxiliary portions of different electrical resistance per unit of length secured at it higher resistance end on the other terminal post to open the contacts upon heating above a predetermined temperature by current flowing in the contacts, the high resistance portion being disposed in oppositely acting relation to the low resistance portion to cause an increase in pressure on the contacts when heated below the opening temperature, the low resistance portion of the strip being bent into a U shape with one arm longer than the other carrying the movable contact and the auxiliary high resistance oppositely acting portion of the strip being relatively straight with one end of the auxiliary portion supporting the shorter arm of the lower resistance main portion in close parallel relation.

4. An overload circuit breaker having a movable contact, terminal posts and a contact fixed to one of the terminal posts, in combination with an integral bimetallic strip formed with a main contact opening portion and an auxiliary contact closing portion secured in heat and electrical conducting relation to the main portion and directly in heat and electrical conducting relation to the other of said terminal posts, the auxiliary portion having a substantially higher resistance per unit of length than the main portion.

5. An overload circuit breaker having a movable contact, terminal posts and a contact fixed to one of the terminal posts, in combination with an integral bimetallic strip formed with a main contact opening portion and an auxiliary contact closing portion secured in heat and electrical conducting relation to the main portion and directly in heat and electrical conducting relation to the other of said terminal posts, the auxiliary portion having a substantially higher resistance per unit of length than the main portion but being of shorter length than the main portion.

6. An overload circuit breaker having a movable contact, terminal post and a contact fixed to one of the terminal posts, in combination with an integral bimetallic strip formed with a main contact opening portion and an auxiliary contact closing portion secured in heat and electrical conducting relation to the main portion and directly in heat and electrical conducting relation to the other of said terminal posts, the auxiliary portion having a substantially higher resistance per unit of length than the main portion, the main contact opening portion of the strip being bent into a U-shape and having the movable contact secured to one arm of the U at the inner side thereof.

7. An overload circuit breakerhaving a movable contact, terminal posts and a contact fixed to one of the terminal posts, in combination with an integral bimetallic strip formed with a main contact opening portion and an auxiliary contact closing portion secured in heat and electrical conducting relation to the main portion and directly in heat and electrical conducting relation to the other of said terminal posts, the auxiliary portion having a substantially higher resistance per unit of length than the main portion, the main contact opening portion of the strip being bent into a U-shape with arms of unequal length and with the movable contact secured to the longer arm.

MORRIS B. WOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,755,043 Alseth et al Apr. 15, 1930 1,825,811 Nelson Oct. 6, 1931 2,118,647 Hottenroth, Jr. May 24, 1938 2,248,387 Rosing et a1. July 8, 1941 2,277,895 Willat Mar. 31, 1942 2,303,153 Woodworth Nov. 24, 1942 2,338,474 Wilson Jan. 4, 1944 2,343,172 Cook Feb. 29, 1944 2,374,022 Lee Apr. 1'7, 1945 2,491,088 Clayton Dec. 13, 1949 

